1. Field of the Invention
The present invention relates to a charge forming apparatus for feeding a fuel/air mixture to an internal combustion engine and, more particularly, to a charge forming apparatus or carburetor including means for feeding the amount of fuel required during the period that the engine is idling or running at a low speed or r.p.m. and means for feeding an amount of air to provide a given r.p.m. to the engine during idling.
2. Description of the Prior Art
As well-known from, e.g., U.S. Pat. Nos. 3,085,791 and 3,404,872 specifications, charge forming apparatus include an idling orifice and a low speed orifice which are open in a mixing passage upstream and downstream of a throttle valve in a closed position and a supplemental fuel passage for guiding fuel to these orifices for the purpose of feeding the amount of fuel required during the period that the engine is idling or running at a low r.p.m.
Most of the charge forming apparatus for feeding a fuel/air mixture to an automotive engine include a bypass open in a mixing passage downstream of a throttle valve to keep the engine running at a low r.p.m. and idling, when loads are generated by, e.g., the operation of an air conditioner during engine idling. This bypass serves to feed air to the engine without being controlled by the throttle valve from any place from an air cleaner to the throttle valve, and is provided with a manually operable valve for the regulation of the flow rate of air.
When said throttle valve is located in the closed position, say, the engine is idling, the fuel is supplied from said idling orifice, and the flow rate of the fuel supplied depends upon how much negative pressure acts on the idling orifice.
Where the engine is used in, e.g., a cold district, on the other hand, it is required to make the r.p.m. of the engine during idling higher than normal. To that end, said manual valve should be operated to sufficiently increase the rate of air flowing through the bypass.
However, when a large amount of air is guided to the downstream side of the throttle valve through the bypass, it is impossible to increase the rate of fuel supplied from the idling orifice in correspondence to said large amount of air by reason of its limited diameter, resultling in the mixture becoming so lean that the r.p.m. of the engine drops.